Covalent organic framework and preparation method thereof

Abstract

The invention discloses a covalent organic framework and a preparation method thereof, and relates to the technical field of semiconductor materials, and the preparation method of the covalent organic framework comprises the following steps: providing a non-metal substrate, and depositing precursor molecules of the covalent organic framework COFs on the non-metal substrate; depositing a metal catalyst on the precursor molecules; heating the precursor molecules to prepare metal catalyst loaded COFs (Covalent Organic Frameworks); and carrying out heating and annealing treatment on the metal catalyst loaded COFs to prepare the COFs. The technical problems that in the preparation process of the COFs material, the electronic state and band gap conditions of the COFs material are difficult to observe, and optimization of COFs synthesis steps and material performance is affected are solved.

Description

Technical Field

[0001] The present application relates to the technical field of semiconductor materials, and in particular to a covalent organic framework and a preparation method thereof. Background Art

[0002] In the synthesis of conventional two-dimensional covalent organic frameworks (COFs), surface-assisted Ullmann coupling reactions usually rely on metal substrates. Metal substrates not only promote efficient molecular organization, but also serve as ideal surface-assisted catalysts to promote Ullmann coupling reactions at high temperatures. However, there is a strong π-electron coupling between the metal substrate and the organic molecules, which leads to a shielding effect of the electronic state of COFs, making it difficult to observe and regulate the electronic state and band gap of COFs, which in turn affects the optimization of COFs synthesis steps and material properties.

[0003] The above contents are only used to assist in understanding the technical solution of the present application and do not constitute an admission that the above contents are prior art. Summary of the invention

[0004] The main purpose of this application is to provide a covalent organic framework and a preparation method thereof, aiming to solve the technical problem that it is difficult to observe the electronic state and band gap of COFs materials during their preparation, which affects the optimization of COFs synthesis steps and material properties.

[0005] To achieve the above object, the present invention provides a method for preparing a covalent organic framework, comprising the following steps:

[0006] Providing a non-metal substrate, and depositing precursor molecules of covalent organic frameworks (COFs) on the non-metal substrate;

[0007] depositing a metal catalyst on the precursor molecule;

[0008] Heating the precursor molecules to obtain COFs supported by metal catalysts;

[0009] The COFs loaded with the metal catalyst are subjected to heating and annealing treatment to obtain COFs.

[0010] In one embodiment, the material of the non-metal substrate includes at least one of highly ordered pyrolytic graphite HOPG, hexagonal boron nitride H—BN, MoS 2 and TiO 2 .

[0011] In one embodiment, the metal catalyst includes at least one of iron, gold, silver, platinum, aluminum, magnesium, tin, copper and nickel.

[0012] In one embodiment, the molecular source of the precursor molecule includes at least one of tris(4-iodophenyl)benzene, 1,3,6,8-tetrabromopyrene, tetrakis-(4-bromophenyl)ethylene and 2,4,6-tris-(4-bromomethyl-phenyl)-[1,3,5]triazine.

[0013] In one embodiment, the heating temperature of the precursor molecules is 350-400° C., and the heating time is 2-8 min.

[0014] In one embodiment, the temperature of the heating annealing treatment is 350-400° C., and the duration is 20-120 minutes.

[0015] In one embodiment, the precursor molecules and / or the metal substrate are deposited by thermal evaporation.

[0016] In one embodiment, the substrate temperature during the thermal evaporation deposition is 180-220° C., the deposition time is 5-100 min, and the vacuum degree is less than or equal to 1×10 -8 mbar.

[0017] The embodiment of the present application also provides a covalent organic framework, which is prepared by the above method.

[0018] In one embodiment, the covalent organic framework has a hexagonal lattice structure.

[0019] One or more technical solutions proposed in this application have at least the following technical effects: Provide a method for preparing a covalent organic framework, by using a non-metallic substrate to replace a metal substrate to deposit the precursor molecules of the covalent organic framework COFs, effectively avoiding the electronic state shielding problem caused by metal-organic coupling, so that the electronic state and band gap of COFs can be observed in time during the preparation process of COFs, and in turn guide the synthesis steps of COFs. Then, a metal catalyst is deposited on the precursor molecule, and the precursor molecule is heated to promote the precursor molecule to undergo a coupling reaction, and epitaxially grow along the substrate surface to obtain COFs loaded with a metal catalyst; through the deposition of the metal catalyst, the Ullmann coupling reaction is promoted, effectively overcoming the defect that the interaction between the precursor molecules of the non-metallic substrate COFs is weak, resulting in the difficulty of surface polymerization reaction. Then, the COFs loaded with the metal catalyst are heated and annealed to remove the metal catalyst loaded on the surface of the COFs, and the COFs whose electronic state and band gap can be observed and regulated are obtained to meet different application requirements. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a flow chart of the method for preparing a covalent organic framework according to an embodiment of the present application;

[0021] Figure 2This is a schematic diagram of the characterization results of HOPG in Example 1 of the present application;

[0022] Figure 3 The characterization results of Example 1 of this application are shown in FIG. Figure 1 ;

[0023] Figure 4 The characterization results of Example 1 of this application are shown in FIG. Figure 2 ;

[0024] Figure 5 The characterization results of Example 1 of this application are shown in FIG. Figure 3 ;

[0025] Figure 6 This is a schematic diagram of the characterization results of Comparative Example 1 of the present application.

[0026] The realization of the purpose, functional features and advantages of this application will be further explained in conjunction with embodiments and with reference to the accompanying drawings. DETAILED DESCRIPTION

[0027] In order to make the purpose, technical scheme and advantages of the embodiments of the present application clearer, the technical scheme in the embodiments of the present application will be described clearly and completely below. If the specific conditions are not specified in the embodiments, they are carried out according to the conventional conditions or the conditions recommended by the manufacturer. If the manufacturer is not specified for the reagents or instruments used, they are all conventional products that can be purchased commercially.

[0028] Hereinafter, the covalent organic framework of the present application and the method for preparing the same are described in detail with appropriate reference to the accompanying drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there are cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structure are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following description are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0029] The "range" disclosed in the present application is defined in the form of a lower limit and an upper limit, and a given range is defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundaries of the particular range. The range defined in this way can be inclusive or exclusive of the end values, and can be arbitrarily combined, that is, any lower limit can be combined with any upper limit to form a range. For example, if a range of 60 to 120 and 80 to 110 is listed for a particular parameter, it is understood that a range of 60 to 110 and 80 to 120 is also expected. In addition, if the minimum range values ​​1 and 2 are listed, and if the maximum range values ​​3, 4 and 5 are listed, the following ranges can all be expected: 1 to 3, 1 to 4, 1 to 5, 2 to 3, 2 to 4 and 2 to 5. In the present application, unless otherwise specified, the numerical range "a to b" represents an abbreviation of any real number combination between a and b, where a and b are both real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" are listed in this document, and "0-5" is just an abbreviation of these numerical combinations. In addition, when a parameter is expressed as an integer ≥ 2, it is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0030] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0031] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0032] If there is no special explanation, all steps of the present application can be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), which means that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), which means that step (c) may be added to the method in any order. For example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0033] If there is no special explanation, the "include" and "comprising" mentioned in this application are open-ended or closed-ended. For example, the "include" and "comprising" may mean that other components not listed may also be included or only the listed components may be included or only the listed components may be included.

[0034] If not specifically stated, in this application, the term "or" is inclusive. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, any of the following conditions satisfies the condition "A or B": A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0035] In order to make the above-mentioned purposes, features and advantages of the present application more obvious and understandable, the technical solution of the present application is further described below in conjunction with the accompanying drawings and embodiments. However, the present application is not limited to the listed embodiments, and should also include any other known changes within the scope of the rights claimed in the present application.

[0036] The term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present application. The term "in one embodiment" that appears in different places in this specification does not necessarily refer to the same embodiment, nor does it refer to a separate or selective embodiment that is mutually exclusive with other embodiments.

[0037] In order to better understand the technical solution of the present application, a detailed description will be given below in conjunction with the accompanying drawings and specific implementation methods.

[0038] Two-dimensional covalent organic frameworks (COFs) materials have great potential as key components of highly selective and highly sensitive biosensors due to their large surface area, adjustable pore structure, and rich electronic properties. They have attracted much attention in the field of surface science.

[0039] In the synthesis of conventional two-dimensional covalent organic frameworks (COFs), surface-assisted Ullmann coupling reactions usually rely on metal substrates. Metal substrates not only promote efficient molecular organization, but also serve as ideal surface-assisted catalysts to promote Ullmann coupling reactions at high temperatures. However, there is a strong π-electron coupling between metal substrates and organic molecules, which leads to the shielding effect of the electronic state of COFs, making it difficult to observe and regulate the electronic state and band gap of COFs, which in turn affects the optimization of COFs synthesis steps and material properties. In addition, when making functional COFs films for devices, metal substrates cannot be used directly as device substrates. Therefore, a complex and tedious transfer process (dry or wet) is required, which introduces impurities and structural defects. To overcome these challenges, researchers have explored methods for the direct synthesis of two-dimensional COFs on non-metallic substrates. The use of non-metallic substrates can avoid the problems caused by metal-organic coupling, while simplifying the synthesis process and reducing impurities and structural defects in the transfer process. However, the interaction between non-metallic substrates and precursors is usually weak, which makes it difficult for molecules to be effectively adsorbed and activated, thereby inhibiting the surface polymerization reaction.

[0040] The present application provides a solution, specifically, a method for preparing a covalent organic framework, by using a non-metallic substrate to replace a metal substrate to deposit the precursor molecules of the covalent organic framework COFs, effectively avoiding the electronic state shielding problem caused by metal-organic coupling, so that the electronic state and band gap of COFs can be observed in time during the preparation process of COFs, and in turn guide the synthesis steps of COFs. Then, a metal catalyst is deposited on the precursor molecule, and the precursor molecule is heated to promote the precursor molecule to undergo a coupling reaction, and epitaxially grow along the substrate surface to obtain COFs loaded with a metal catalyst; by the deposition of the metal catalyst, the Ullmann coupling reaction is promoted, effectively overcoming the weak interaction between the precursor molecules of the non-metallic substrate COFs, which makes it difficult to carry out the surface polymerization reaction. Then, the COFs loaded with the metal catalyst are heated and annealed to remove the metal catalyst loaded on the surface of the COFs, and the COFs whose electronic state and band gap can be observed and regulated are obtained to meet different application requirements.

[0041] Reference Figure 1 The first aspect of the embodiment of the present application provides a method for preparing a covalent organic framework, comprising the following steps:

[0042] Step S10, providing a non-metal substrate, and depositing precursor molecules of covalent organic frameworks (COFs) on the non-metal substrate;

[0043] In one feasible embodiment, in order to avoid the problem of COFs electronic state shielding caused by metal-organic coupling, a non-metallic substrate is used, and the precursor molecules of the covalent organic framework COFs are deposited on the non-metallic substrate to achieve the synthesis of a self-assembled two-dimensional porous monolayer structure on the substrate surface.

[0044] For example, the non-metal substrate may be subjected to a surface cleaning treatment before use, the surface contamination layer may be removed by hand tearing, and then subjected to a heating annealing treatment.

[0045] In a feasible embodiment, the material of the non-metal substrate includes at least one of highly ordered pyrolytic graphite HOPG, hexagonal boron nitride H—BN, MoS 2 and TiO 2 .

[0046] HOPG is a new type of graphite material obtained by high temperature and high pressure treatment. Its performance is close to that of single crystal graphite, and it has the characteristics of high purity, high crystallinity and high orientation. These characteristics make the HOPG surface have very low roughness (usually less than 0.1nm), so it can provide a smooth, uniform and defect-free substrate for the growth of COFs materials. At the same time, HOPG has the smallest lattice mismatch with various organic molecules, and is relatively stable chemically and not easy to react with reactants, thus ensuring the chemical stability of COFs materials during the growth process. In addition, the HOPG surface also has a standard hexagonal atomic order arrangement and excellent conductivity. Therefore, it can meet the conductivity requirements of various tests for the substrate, and will not produce strong coupling with the material to affect the electronic state research of COFs, which is very suitable for high-resolution characterization and imaging. This helps to accurately characterize and analyze the microstructure and properties of COFs materials after preparing them.

[0047] H-BN is an ideal substrate material due to its atomically flat surface and chemical inertness.

[0048] MoS2 and TiO2 are commonly used inert semiconductor substrates.

[0049] Exemplary materials of the non-metal substrate include highly ordered pyrolytic graphite HOPG, hexagonal boron nitride H-BN, MoS2 or TiO2.

[0050] Preferably, the material of the non-metal substrate includes: highly ordered pyrolytic graphite HOPG.

[0051] Exemplary molecular sources of precursor molecules include: halogenated aromatic compounds.

[0052] In one possible embodiment, the molecular source of the precursor molecule includes at least one of tris(4-iodophenyl)benzene TIB, 1,3,6,8-tetrabromopyrene, tetrakis-(4-bromophenyl)ethylene and 2,4,6-tris-(4-bromomethyl-phenyl)-[1,3,5]triazine.

[0053] For example, the use of TIB can ensure that COFs form hexagonal lattice pores by coupling benzene rings, and this hexagonal structure is the most stable and has the largest number in large-area preparations, which is consistent with experimental facts.

[0054] For example, before depositing the precursor molecules of COFs, the molecular source of the precursor molecules is heated for 1-2 days to slowly evaporate small molecular impurities with low evaporation temperature in the molecular source to obtain a pure molecular source.

[0055] In one possible embodiment, the precursor molecules of COFs are deposited on a non-metallic substrate by thermal evaporation.

[0056] Exemplarily, the substrate temperature when depositing the precursor molecules of COFs is 180-220° C., for example, 180° C., 185° C., 190° C., 195° C., 200° C., 205° C., 210° C., 215° C., 220° C., etc. At this temperature, the molecular source can be successfully evaporated.

[0057] Exemplarily, the deposition time of the precursor molecules of the deposited COFs is 5 to 100 min, for example, 5 min, 10 min, 20 min, 30 min, 40 min, 50 min, 60 min, 70 min, 80 min, 90 min, 100 min, etc. Within this time, a monolayer or a few layers of molecular coverage can be obtained on the non-metallic substrate.

[0058] For example, ultra-high vacuum conditions are required when depositing COFs precursor molecules, and the vacuum degree is less than or equal to 1×10 -8 mbar. Deposition under vacuum conditions can significantly improve the quality of single-layer materials.

[0059] Step S20, depositing a metal catalyst on the precursor molecule;

[0060] In one possible embodiment, a metal catalyst may be further deposited on the precursor molecules by thermal evaporation.

[0061] Exemplarily, the substrate temperature during deposition of the metal catalyst is 180-220°C; for example, 180°C, 185°C, 190°C, 195°C, 200°C, 205°C, 210°C, 215°C, 220°C, etc.

[0062] Exemplarily, the deposition time of the deposited metal catalyst is 5 to 100 min; for example, 5 min, 10 min, 20 min, 30 min, 40 min, 50 min, 60 min, 70 min, 80 min, 90 min, 100 min, etc.

[0063] For example, ultra-high vacuum conditions are required when depositing metal catalysts, and the vacuum degree is less than or equal to 1×10 - 8 mbar.

[0064] In one feasible embodiment, the metal catalyst includes at least one of iron, gold, silver, platinum, aluminum, magnesium, tin, copper and nickel. By depositing the metal catalyst, the occurrence of the Ullmann coupling reaction at high temperature is promoted, that is, the dehalogenation and polymerization of the halogenated aromatic compound, thereby forming a stable CC bond and constructing COFs.

[0065] Step S30, heating the precursor molecules to obtain COFs supported by metal catalysts;

[0066] In one feasible embodiment, the precursor molecules are heated to promote the occurrence of the Ullmann dehalogenation carbon-carbon coupling reaction, so that the crystal structure units of COFs grow epitaxially along the substrate surface to obtain large-area single-layer two-dimensional COFs loaded with metal catalysts.

[0067] In one feasible embodiment, the heating temperature when heating the precursor molecules is 350-400°C; for example, 350°C, 355°C, 360°C, 365°C, 370°C, 375°C, 380°C, 385°C, 390°C, 395°C, 400°C, etc.

[0068] In one feasible embodiment, the heating time when heating the precursor molecule is 2 to 8 min; for example, 2 min, 2.5 min, 3 min, 3.5 min, 4 min, 4.5 min, 5 min, 5.5 min, 6 min, 6.5 min, 7 min, 7.5 min, 8 min, etc.

[0069] Step S40, heating and annealing the COFs loaded with the metal catalyst to obtain COFs.

[0070] In a feasible embodiment, COFs loaded with metal catalysts are subjected to heating annealing treatment to remove the metal catalysts and halogen elements loaded on the surface of COFs to obtain COFs.

[0071] In one feasible embodiment, the temperature during the heating annealing treatment is 350-400°C; for example, 350°C, 355°C, 360°C, 365°C, 370°C, 375°C, 380°C, 385°C, 390°C, 395°C, 400°C, etc.

[0072] In a feasible implementation manner, the duration of the heating annealing treatment is 20 to 120 min; for example, 20 min, 30 min, 40 min, 50 min, 60 min, 70 min, 80 min, 90 min, 100 min, 110 min, 120 min, etc.

[0073] In one feasible embodiment, the prepared COFs have a hexagonal lattice structure and are stable.

[0074] In this embodiment, the precursor molecules of the covalent organic framework COFs are deposited by using a non-metal substrate instead of a metal substrate, which effectively avoids the electronic state shielding problem caused by metal-organic coupling, so that the electronic state and band gap of COFs can be observed in time during the preparation process of COFs, and in turn guide the synthesis steps of COFs. Then, a metal catalyst is deposited on the precursor molecule, and the precursor molecule is heated to promote the coupling reaction of the precursor molecule, and epitaxial growth is achieved along the surface of the substrate to obtain COFs loaded with a metal catalyst; through the deposition of the metal catalyst, the Ullmann coupling reaction is promoted, and the weak interaction between the precursor molecules of the non-metallic substrate COFs is effectively overcome, resulting in the defect that the surface polymerization reaction is difficult to carry out. Then, the COFs loaded with the metal catalyst are heated and annealed to remove the metal catalyst loaded on the surface of the COFs, and the COFs whose electronic state and band gap can be observed and regulated are obtained to meet different application requirements.

[0075] In order to enable the details and operations of the above embodiments of the present application to be clearly understood by those skilled in the art, and to significantly demonstrate the improved performance of the embodiments of the present application, the above technical solutions are illustrated by means of multiple embodiments below.

[0076] Example 1

[0077] (1) providing a HOPG substrate (non-metallic substrate), heating and annealing the HOPG substrate at 500° C. to obtain a clean HOPG substrate, such as Figure 2 As shown;

[0078] (2) TIB (molecular source of precursor molecules) was heated at 120°C for 2 days to remove impurities and purify, and TIB precursor molecules were deposited on the HOPG substrate by thermal evaporation, wherein the substrate temperature of the thermal evaporation was 180°C, the deposition time was 5 min, and the vacuum degree was 1×10 -8 mbar; in situ imaging of the samples was performed by low-temperature high-resolution scanning tunneling microscopy (LT-STM), such as Figure 3 As shown, the self-assembly behavior of TIB precursor molecules was observed, indicating that the TIB precursor molecules have been successfully evaporated on the surface of the HOPG substrate;

[0079] (3) Depositing iron (metal catalyst) on the surface of TIB precursor molecules by thermal evaporation, wherein the substrate temperature of thermal evaporation is 180°C, the deposition time is 5 min, and the vacuum degree is 1×10 --8 mbar;

[0080] (4) The HOPG substrate was heated at 400°C for 5 min to promote the Ullmann coupling reaction. The chemical reaction formula is as follows:

[0081]

[0082] (5) Heat annealing at 400°C for 50 min to remove iron and iodine to obtain COFs; perform in situ imaging of the samples using LT-STM, such as Figure 4 As shown, it was observed that COFs have a hexagonal lattice structure and there are lattice units with different pore sizes.

[0083] Comparative Example 1

[0084] (1) providing a gold substrate (metal substrate), and heating and annealing the gold substrate at 500° C. to obtain a clean gold substrate;

[0085] (2) TIB (molecular source of precursor molecules) was heated at 120°C for 2 days to remove impurities and purify, and TIB precursor molecules were deposited on a gold substrate by thermal evaporation, wherein the substrate temperature of the thermal evaporation was 180°C, the deposition time was 5 min, and the vacuum degree was 1×10 -8 mbar;

[0086] (3) The gold substrate was heated at 400 °C for 5 min to promote the Ullmann coupling reaction and obtain COFs.

[0087] The COFs prepared in Example 1 and Comparative Example 1 were characterized by in-situ imaging using LT-STM. The results are as follows: Figure 5 and 6 As shown, Figure 5 Schematic diagram of the structure of COFs prepared in Example 1 at different magnifications ( Figure 5 (a) to Figure 5 (c) Enlarged size in order of increasing), Figure 6 Schematic diagram of the structure of COFs prepared in Comparative Example 1. (It should be understood that Figure 4 and 5All are characterization diagrams of COFs prepared in Example 1. Due to the difference in image display parameters between the two, there are certain differences in the display effects. It can be seen that there are obvious differences between COFs on HOPG substrate and COFs on gold substrate. Since Comparative Example 1 uses a metal substrate, metal-organic coupling will produce electronic state shielding problems during the preparation of COFs, making it difficult to observe the electronic state and band gap of COFs. In Example 1 of the present application, the HOPG substrate will not produce electronic state shielding for COFs, so the band gap and electronic state of the material can be characterized while preparing, and in turn guide the synthesis steps to obtain materials with continuously adjustable band gaps to meet different application requirements.

[0088] The above are only preferred embodiments of the present application, and do not limit the scope of the present application. For those skilled in the art, the present application may have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the scope of patent protection of the present application.

Claims

1. A method for preparing a covalent organic framework, characterized in that: The method comprises the following steps: Providing a non-metal substrate, and depositing precursor molecules of covalent organic frameworks (COFs) on the non-metal substrate; depositing a metal catalyst on the precursor molecule; Heating the precursor molecules to obtain COFs supported by metal catalysts; The COFs loaded with the metal catalyst are subjected to heating and annealing treatment to obtain COFs.

2. The method according to claim 1, characterized in that The material of the non-metal substrate includes at least one of highly ordered pyrolytic graphite HOPG, hexagonal boron nitride H-BN, MoS2 and TiO2.

3. The method according to claim 1, characterized in that The metal catalyst includes at least one of iron, gold, silver, platinum, aluminum, magnesium, tin, copper and nickel.

4. The method according to claim 1, characterized in that The molecular source of the precursor molecule includes at least one of tri(4-iodophenyl)benzene, 1,3,6,8-tetrabromopyrene, tetrakis-(4-bromophenyl)ethylene and 2,4,6-tris-(4-bromomethyl-phenyl)-[1,3,5]triazine.

5. The method according to claim 1, characterized in that The heating temperature when heating the precursor molecules is 350-400° C., and the heating time is 2-8 minutes.

6. The method according to claim 1, characterized in that The temperature of the heating annealing treatment is 350-400° C. and the duration is 20-120 minutes.

7. The method according to claim 1, characterized in that The precursor molecules and / or the metal substrate are deposited by thermal evaporation.

8. The method according to claim 7, characterized in that The substrate temperature during the thermal evaporation deposition is 180-220° C., the deposition time is 5-100 min, and the vacuum degree is less than or equal to 1×10 -8 mbar.

9. A covalent organic framework, characterized in that The covalent organic framework is prepared by the method according to any one of claims 1 to 8.

10. The covalent organic framework according to claim 9, characterized in that The covalent organic framework has a hexagonal lattice structure.

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